patent pertains to the field of hydrophones, and especially to arrays of hydrophones for use as towed active sensing devices. Such arrays are used to perform active sound imaging, and depend on a plurality of spaced, active sonic transducers at a controlled spacing for providing data which cannot be obtained readily from a single hydrophone.
U.S. Pat. No. 4,733,379 to Lapetina et al, discloses a form of towed hydrophone array of a type being a uniform diameter linear tube containing individual hydrophone transducers periodically spaced therein. This patent places great emphasis on acoustic cross coupling between each of the transducers. The transducers shown in the preferred drawing are orthogonal to each other, rotated at 90 degree angles.
Massa, U.S. Pat. No. 2,440,903 is an earlier towed array patent again showing a hose type streamer, and specifically claiming the interior, periodic structure of a transverse transducer and window, described internally as being flush with the hose for minimum turbulence. Despite this FIG. 1 discloses a structure No. 21 which is never used in the Art, primarily because any such protuberance would produce excessive noise.
In terms of towed, fish shaped or streamlined sensors, an early patent, U.S. Pat. No. 1,487,138 to Atwood, discloses a single towed elongate structure with tapered ends. At the time of this patent specifically the Art considered that the proper means of reducing the noise due to the rush of water past the towed article (the "fish") was by deployment at either a very low speed or zero forward speed with relative to the water. Despite the introduction of the uniform external cross-section tube, current towed arrays are still severely speed limited because of noise effects.
U.S. Pat. No. 3,842,398 to Massa shows, incident to an invention involving the interconnection of a hydrophone and a towed, expendable velocimeter, a construction for a towed hydrophone array showing a bulbous shaped hydrophone attached to a cable. The hydrophone is described as being embedded in a rigid potting compound, coated with a rubber or rubber-like coating and forming a blended streamline attachment to the outer jacket of the cable.
U.S. Pat. No. 3,990,035 to Byers discloses a hydrodynamically streamlined sonar apparatus. The housing shape is specifically described as being substantially oval in cross section through the length of the object and circular in cross section transverse to the direction of towing. The shape is further restricted to being a Joukowski streamlined shape and the housing is described as being principally rigid solid material. All the transducers of the array are enclosed in but a single housing.
U.S. Pat. No. 3,611,276 to Massa describes one of the velocimeters cited in Donald Massa's above cited U.S. Patent. Massa discloses a particular shape for free falling velocimeter having a predictable fixed rate of fall. Further the dropped device is a transmitter; therefore, there is no particular consideration for sensitivity or noise. Massa does describe the dimension of the streamlined probe with respect to the wave length of the sound waves concerned (note Column 4, line 65-75). Massa's shape is intended to achieve a stable free fall rate; turbulence effects are not addressed.
U.S. Pat. No. 4,031,502 to Lefaudeux, et al and U.S. Pat. No. 4,709,361 to Dahlstrom, et al are also of interest for the design of sensor shapes.
My prior U.S.Pat. No. 4,958,329, incorporated herein by reference, teaches and discloses a construction and hydrodynamic shape for a hydrophone body which has significantly reduced turbulence noise at the location of the hydrophone sensor. This body permits the construction of hydrophone arrays interconnected by thinner, more flexible cables than the prior art.